1. Field of the Invention
The invention relates to a still image filing system for compressing still image data and recording onto a recording medium and for reading out the recorded data from the recording medium and reconstructing the still image data.
2. Description of the Related Art
There is a still image filing system in which still image data is compressed and recorded as a file onto a disk and the data read out from the disk can be reconstructed as still image data. For instance, as shown in FIG. 1, an analog video signal showing a still image is supplied from an input terminal AIN to an A/D converter 1 and converted into a digital signal. The digital signal is once written as still image data into a frame memory 2 through a switch SW. When still image data is supplied to an input terminal DIN, it is directly written into the frame memory 2 through the switch SW. The written still image data is read out from the frame memory 2 and compressed by a compressor 3. The compression is executed on the basis of a method specified by, for instance JPEG (Joint Photographic Experts Group). The still image compression data generated from the compressor 3 is supplied to a disk drive 4 and written onto the disk. The writing and reading operations of the disk drive 4 are instructed by a microcomputer (not shown). In case of reproducing an analog video signal indicative of a still image from the data recorded on the disk, the switch SW is switched and an output of a reconstructing device 5 is relay-connected to the frame memory 2. When the disk drive 4 reads out the written still image compression data from the disk, the data is supplied to the reconstructing device 5. The reconstructing device 5 reconstructs the still image compression data to the still image data by an expanding operation opposite to the compressing operation of the compressor 3. The reconstructed still image data is written into the frame memory 2 through the switch SW. After that, it is read out from the frame memory 2 and supplied to a D/A converter 6. A reproduction analog video signal from the D/A converter 6 is generated from an output terminal OUT to a display device (not shown) such as a CRT display or the like.
In such a still image filing system, however, the data is recorded on the recording medium such as a disk or the like without checking a deterioration of a still video image due to the data compressing operation in the compressor 3 in the data recording mode. Particularly, there is a case where a method in which data cannot be completely reconstructed the JPEG standard is used as a compressing method. In such a case, the deterioration of the still video image due to the compression needs to be checked in the recording mode.
In case of editing the still image data recorded on the disk and then recording to another disk, two still image filing systems are ordinarily used. The data recorded on the disk by one of the still image filing systems is reproduced as an analog video signal, the analog video signal is transferred to the other still image filing system and is again compressed, and after that, the compressed signal is recorded to another disk.
When the method in which the data cannot be perfectly reconstructed as mentioned above is used as a compressing method, although a deterioration of the still video image due to a single compressing and reconstructing process is inconspicuous, by repeating the compressing and reconstructing process many times, the deterioration of the still video image becomes conspicuous. It is, therefore, desirable to avoid a method such that the recorded still image compression data is once reproduced as an analog video signal and, thereafter, it is again compressed and recorded onto the recording medium.
In case of directly recording the digital video signal as it is, further, since there are non-compression data and compression data as digital video signals, prior to editing, the user needs to previously check whether the still video image recorded on the recording medium has been recorded as compression data or not.